This invention relates to refrigeration systems and, while of other utility, is particularly adapted to such systems for cooling the passenger compartments of automotive vehicles, systems for air conditioning recreational vehicles, systems for cooling portable refrigerators for recreational vehicles, and systems for refrigerating cargo transporters.
In some of the prior systems of the type mentioned, there is typically provided a compressor driven by a vehicle engine through a suitable belt and pulley power take-off. Such a system is inherently wasteful of energy. For example, in many, if not all, automotive applications, the desired degree of cooling is determined for vehicle idling conditions, typically at engine speeds around 600 r.p.m., whereas when the vehicle engine is running at full speed, it may be rotating at 3000 r.p.m. or more. Therefore, it can be seen that the resultant cooling will vary significantly as the engine speed changes. For example, when the vehicle is moving with its engine rotating at an increased speed, the compressor is driven at a significantly higher speed as compared to idling speed. The cooling achieved at the higher vehicle engine speed is typically greater than that required. For these and other reasons, such refrigeration systems comprise compressors of greater capacity and therefore cost, than that required, since a high capacity is needed for idling conditions, although excess capacity exists during normal running periods.
A significant disadvantage of such refrigeration systems is that the excess cooling places a penalty upon the gas mileage of the vehicle. In larger vehicles, the gas mileage penalty has been estimated to be in the order of 10%, whereas in smaller vehicles with smaller engines, the penalty may be even greater. Further, the extra power requirements placed upon the vehicle engine, especially that of a smaller car, present a potential safety hazard in that the accelerating capacity of such a vehicle is significantly reduced when its air conditioning system is in operation.
To compensate for variations, and in particular for increase of the vehicle engine speed, it has been a typical practice to provide bypass means that is selectively operable to regulate the cooling operation of the system's evaporator in accordance with temperatures desired in the compartment to be cooled. However, such apparatus is subject to very high pressure differentials, with consequent leakage as well as the need for very strong mechanical linkages to operate the bypass means which typically take the form of bypass valves.
Further attempts have been made to compensate for the excess capacity of such refrigeration systems by heating the cooled air to be circulated into the passenger compartment of the automotive vehicle. It is apparent that such a process places a double penalty upon the gas mileage of the vehicle motor when so operated. Further, a mechanical device such as a clutch may be inserted between the vehicle motor and the compressor which is cycled ON and OFF to achieve the desired temperature within the passenger compartment. Such a system places a high strain upon not only the clutch so inserted, but also upon the compressor. For example, if the vehicle engine is operated at 3000 r.p.m. and the compressor is at a standstill when the clutch is engaged, the compressor must accelerate at a rapid rate, thus placing an extreme degree of mechanical strain upon the compressor and clutch. When the clutch is of the electromagnetic type, power loss and energy drain is also caused by such clutch.
The periodic turning ON and OFF of an automotive air conditioning refrigeration system causes temperature variations noticeable to the passengers. In typical automobiles, the cooling loss, particularly through the vehicle windows, is quite rapid on a hot day, so that passenger comfort is significantly affected by rapid heating-up and cooling-down of the air within the passenger compartment.
A further problem arising from the mechanical coupling of a vehicle air conditioning system to the vehicle's motor, is that the air conditioning system typically is mounted upon the engine, and that an externally driven shaft must pass through a compressor housing seal so as to drive the compressor. Due to mounting on or near the engine, the vehicle air conditioning system is subjected to considerable vibration. Such air conditioning systems are sealed so that the coolant (typically freon) will not leak. When subjected to such vibration of the vehicle motor, the various seals of the air conditioning system and in particular the seals provided about the compressor shaft, begin to break down and eventually, the coolant escapes.
Similar problems to those described above with respect to automotive vehicle air conditioning systems, exist for RV's (recreational vehicles), many of which are equipped with air conditioning and portable refrigerating units. Typically, such RV's may include two air conditioning systems, one coupled mechanically to the vehicle engine to cool the vehicle while the vehicle is moving, and a second air conditioning unit mounted on the roof to be plugged into a standard 115V power outlet, when the vehicle is parked. In the prior art, it has been found to be more convenient to provide two air conditioning systems rather than to adapt a single air conditioning system to be operative while the motor vehicle is running and when it is parked. Most RV refrigerators are of the gas adsorption type which require leveling of the vehicle; the handling of gas; relighting of a pilot light; high manufacturing cost; and relatively high energy input requirements.
In the case of refrigerated trucks, auxiliary gas engines or other conventional prime movers are coupled to separate compressors. With these systems also, reliability may be a problem due to seal leakage, etc.
Some of the above problems have been recognized in the art as indicated, for example, by U.S. Pat. No. 3,634,873 which issued Jan. 11, 1972. The approach of that patent, however, is in serveral respects similar to old techniques. For example, salient pole winding arrangements are utilized, and maximum speed and efficiency appear to be inherently limited because (among other reasons) of a need to rely on mechanical switching mechanisms.